Background: Hepatitis B virus (HBV) is a small enveloped virus that belongs to the hepadnavirus family. The genome of the hepatitis B virus (HBV), a partially doublestranded circular DNA, has four known genes encoding the viral surface proteins (pre-S 1, pre-S2 and HBsAg), the precore (pre-C) and core (C) proteins (HBeAg and HBcAg), the DNA polymerase, the X protein. There are distinct subtypes of HBV indicative of strain heterogeneity. The subtypes are distinguished by antigenic determinants on the surface antigen (HBsAg) and their corresponding antibodies. There is a common group determinant, a, which appears in all HBsAg specimens. There are two sets of subdeterminants, d or y and w or r, which appear to be allelic or mutually exclusive and which are used for the identification of subtypes. Thus, there are at least four major groups into which HBsAg can be classified: adw, adr, ayw, and ayr.